There's currently no battleships between dreanought and bismarck (leander and town don't count cause they're cruisers and they kinda suck) so I propose to add the Ise clas battleship at level 6. This class is considered a late dreadnought to early battleship, perfect as a bridge to bismarck. it would have more firepower, health, and versatility than a dreadnought, but less speed and overall size than a bismarck.
Length: 219.62 m
Draft: 9.03 m
Speed: 25 knots
Health: 7.32
AA: 0.38
Torpedo Resistance: 35%
Armament:
- 8 x 14 inch guns (mounted on 4 twin turrets)
- 6 x AA rocket launchers (irl each launcher had 30 rockets, but maybe 2 each for a total of 12 would be balanced)
- 4 x aircraft (can be same as Yamato for simplicity)
https://en.wikipedia.org/wiki/Japanese_battleship_Ise
Note that the game would use the Ise after its 1943 conversion which included greater speed and aircraft capacity.
Here is a blueprint: https://upload.wikimedia.org/wikipedia/commons/9/9f/Ise1944.png